Solar energy collecting systems broadly include a concentrating, focusing or reflecting means of some type which receives the sun's rays from a predetermined extended area and directs the received solar energy to a collector means of some type which in turn receives the initial energy in an enhanced or concentrated form, specifically at a much higher degree of heat per unit area than originally received by the receiving means. The collector means utilizes the energy which it receives to heat a fluid such as air or water directly for immediate use or stores the same in a heat sump or heat reservoir for ultimate use on demand. The heat energy received by the collector may also be converted to electrical energy for immediate use or converted to electrical energy and stored in storage devices or batteries for ultimate use on demand.
In most instances, the means for receiving the solar energy from the sun is some form of extended receiving surface which focuses the received energy onto a substantially smaller collector means, thus enhancing or concentrating the energy as originally received. Obviously, the receiving means, whether adapted to absorb solar energy directly or reflect it to a collector means must present an extremely large receiving surface in order to provide concentrated or enhanced energy sufficiently hot to be practical for end use.
Most solar energy systems, in use or proposed for use, have been of the type in which an extended reflecting surface receives the solar energy and directs it to a substantially smaller collector means. Such reflecting surfaces may also take a wide variety of forms. For example, flat, dished, parabolic troughs, etc. The system may also be of the tracking or nontracking type, which to a great extent, depends upon the receiving surface. For example, flat receiving surfaces or reflecting surfaces need to be oriented according to the position of the sun in order to receive sufficient energy. Thus, such systems are so-called tracking systems when the receiving surface tracks the movement of the sun from horizon to horizon on a daily basis and, preferably, the azimuthal position of the sun on a seasonal basis. While tracking on a seasonal basis can be performed manually, it is wholly impractical to manually track the sun on a daily basis. Accordingly, automatic tracking systems are provided. Such tracking systems are complex and expensive to operate and maintain. By contrast, a parabolic trough-type receiving means can be utilized as a so-called nontracking systems. By appropriately shaping the parabola and sizing and positioning a collector within the parabola so as to receive substantially all of the energy received by and reflected by the inner reflecting surface of the parabola and correctly positioning the reflector surface in a generally east-west direction, it is unnecessary to track on a daily basis and all that is required for maximum efficiency is changing the orientation several times, for example, two to four times per year, to accommodate seasonal changes of the positions of the sun. Because of the size of the receiving surface necessary, it is obvious that a major portion of the cost of such a system lies in the manufacture, transportation and installation of the receiving surface, particularly where the receiving surface is a reflective surface.
Another cost factor, which generally has not been recognized in the art until after commercial units have been installed, is the rapid deterioration of the receiving surface due to exposure to the elements. Even if the receiving surface is such that it does not permanently deteriorate as a result of exposure to the elements, for example, glass mirrors, collection of dirt and the like on the surface also causes rapid temporary deterioration of the surface and a substantial reduction in efficiency. One solution to this problem has been the provision of automatic cleaner or washing systems. This, of course, adds to the cost of the overall system and there is a limit as to how many times any surface can be cleaned without damaging the surface. Another solution to this problem has been the provision of readily replaceable rigid or semirigid panels. One of the less expensive types of panels that has been proposed has been an extruded rigid or semirigid substrate sheet having a reflective thin film, such as an aluminized polyester film, bonded thereto and, preferably, also having a transparent protective film or coating over the top of the aluminized film. Problems peculiar to this type of structure include finding the right combination of materials which can be bonded together and to which anchoring means can be appropriately attached. It has been found that at least local delamination occurs, believed to be primarily due to moisture collecting between the layers. In any type of rigid or semirigid panel construction, as was previously described, the very size of the panels results in substantial cost of the manufacture, transportation, installation and replacement. The size also creates problems in installation due to the action of the wind on the panels. A still further reduction in costs can be attained by the utilization of flexible, sheet-type reflectors such as an aluminized flexible sheet of polyester. Obviously, initial costs, transportation costs and replacement costs are substantially reduced by this type of receiving surface.
However, the flexible sheet-type surfaces have their own inherent problems. Most of these problems are attributable to the action of the wind during installation and use. Obviously, the sheet must be thick enough to withstand wind forces expected to be encountered in the area where the system is to be located, snow accumulation, rain, hail, etc., without distorting or rupturing the flexible sheet. In general, however, it is believed that flexible polyester sheets of at least about 5 mil thickness can withstand the force of these elements without serious distortion or destruction. For example, such materials are capable of continued operation at wind speeds as high as ten miles per hour. While such material will generally withstand wind speeds above this level, it has been found that the material tends to flutter at these higher wind speeds, thus substantially reducing the receiving efficiency. Finally, in addition to size contributing to problems of installation, the flexible nature of the material further exaggerates the problem.